Cancer is the third most common cause of death in the world according to the World Health Organization, after heart disease and infectious disease. Cancer is the second most common cause of death (after heart disease) in the developed world. Accordingly, discovery of new and effective treatments for cancer is a high priority for health care researchers.
Cancer is often treated by using chemotherapy to selectively kill or hinder the growth of cancer cells, while having a less deleterious effect on normal cells. Chemotherapeutic agents often kill rapidly dividing cells, such as cancer cells; non-malignant cells which are dividing less rapidly are affected to a lesser degree. Other agents, such as antibodies attached to toxic agents, have been evaluated for use against cancers. These agents target the cancer cells by making use of a characteristic specific to the cancer, for example, higher-than-normal rates of cell division, or unique antigens expressed on the cancer cell surface.
As toxic agents specifically targeted against cancer cells can enhance therapeutic efficacy, reduce undesirable side effects, or both, many efforts have been made to achieve selective localization of well-defined chemical materials in malignant tumors. A significant advance in the field occurred with the introduction of tetraphenylporphine sulfonates (TPPS), which are non-naturally occurring porphyrins (Winkelman J. (1962) Cancer Res. 22:589). A hematoporphyrin derivative (HPD) was also found to localize in tumors (Lipson R L, Baldes, E J, & Gray M S (1967) Cancer 20: 2255). HPD is a complex mixture of porphyrins currently used as a sensitizer derivative that concentrates in tumor cells and destroys them after the tumor is irradiated with light or a laser beam (Dougherty T J, (1987) Photochem. Photobiol. 45:879). A wide variety of porphyrins and porphyrin analogues have been found to be selectively taken up by tumors, such as the naturally occurring porphyrins; for example, the octacarboxylic uroporphyrins, the tetracarboxylic coproporphyrins, and the dicarboxylic protoporphyrin. Synthetic porphyrins are also selectively taken up by tumors; among them are the meso-tetraphenyl porphyrins and the different porphyrin sulfonates TPPS4, TPPS3, TPPS2a and TPPS1, which are listed in order of decreasing number of sulfonic acid substituents and decreasing hydrophilicity. Many factors determine the uptake and concentration of porphyrins in the tumors; one important factor is the structure (hydrophobicity, size, polarity) of the drug; another important factor is the formulation in which it is delivered (Sternberg E and Dolphin D (1996) Current Med Chemistry 3, 239). The mechanism(s) of porphyrin localization in tumors is still not entirely clear; the more hydrophobic porphyrins are preferentially incorporated in the lipid core of lipoproteins. Tightly aggregated porphyrins circulate as unbound pseudomicellar structures which can be entrapped in the interstitial regions of the tumor, can be localized in macrophages, or can enter neoplastic cells via pinocytotic processes. Low density lipoproteins (LDL), which are endocytosed by neoplastic cells through a specific receptor-mediated pathway, display the most selective release of porphyrins into the tumors (Jori G (1989) Photosensitizing Compounds, Ciba Foundation Symp 146, pp 78–94).
The present invention describes the synthesis and cytotoxic actions of porphyrin-polyamine conjugates. They are taken up by the tumor cells due to their porphyrin moiety, while the polyamine moiety provides the cytotoxic effects (see International Patent Application Nos. WO 00/66587 and WO 02/10142, and U.S. Pat. Nos. 6,392,098, 5,889,061, and 5,677,350).